Hypothes.is lets visitors annotate your Web pages, via a pop-out sidebar filled with a Twitter-like stream of visitor comments/links.

It’s the perennial idea of re-inventing the classic footer comments box as a uniform annotation layer, something that has been tried many times over the past 20 years. Google ran such a tool for three years before closing it down. Such services tend to end up as dank wastelands filled with Viagra ads, troll spoor and link-rot.

But this time might be different. There’s a couple of somewhat workable-looking early W3C standards (more are on the way), new options for moderation and closed group working, and an impressive range of publishers and universities are now planning to discuss how social annotation might proceed for scholarship…

Our goal is that within three years, annotation can be deployed across much of scholarship.”

The ‘can’, not ‘will’, is probably because the big publishers like Elsevier et al are noticeably absent from the list of Hypothes.is academic supporters. I can’t see them liking the idea that an open commenting system is being laid over/into their content. The sidebar’s content seems to be outside the control of the page owner, so I could theoretically pitch up at an Elsevier $66 article paywall and say “there’s a free PDF of this article over at Site XYZ…”

So how does it work, at present? Imagine that someone took a Web page’s comments section from the bottom of the page, and instead put it into a standalone and uniform sidebar. Someone adding a comment also has the option to highlight a bit of text on the page, automatically hyperlinking their comment to it. Other visitors see the comments and the highlighted text. Obviously various Twitter-ish and Wiki-ish features could be added, but that’s the basic functionality.

A pop-out sidebar means that Hypothes.is can work with PDFs, and the Hypothes.is roadmap suggests that annotation of data / images / videos / ePubs could be on the way soon. So it seems Hypothes.is needs fixed browser-displayed content, located on a URL that’s never going to break — a natural fit with things like PDFs in repositories and digital libraries. But even in that relatively limited arena, who will do all the hand annotation, moderation, linkrot checking and repair need to keep such a service usable across a billion or more pages and documents? I somehow doubt that overworked and underpaid repository staff will be skipping through the library stacks with joy, at being told they must also become the herders of social media cats and the tamers of trolls.